This system will generate 20-ps width pulses useful for precise determination of fluorescence lifetimes. The system consists of a mode-locked argon ion laser which pumps a dye laser, and the output is cavity dumped and frequency doubled, to produce single, 20-ps width pulses, 250-700 nm wavelength, at a high rep rate. The pulse excites a biological sample and the fluorescent photons are collected via a monochromator. The decay of fluorescence is processed by single photon electronics and multi-channel analyzer buffer storage. The data is then transferred into a minicomputer for analysis. The instrument will be employed to continue our study of protein interactions in bioluminescence and to develop this presently rather sophisticated machine into a standard instrument for general use in biochemistry. Special attention will be first given to the interaction of "lumazine protein", the emitter of bacterial bioluminescence with the protein bacterial luciferase. Measusrement of fluorescence lifetimes and anisotropy decay of both the ligand and intrinsic fluorophores will be made. Heterogeneous decay profiles will require superior counting statistics for their unambiguous analysis. Variations of solution conditions, source of proteins, modification reagents, are all known to affect these protein-protein and-ligand interactions, as measured by the lumazine fluorescence and anisotropy decay. More general applications will be studies of protein fluorescence, in particular enolase, the binding of Eu(III) to enolase, and the localization and fluorescence properties of fluorophores in cells such as from adipose tissue, plants and insulin receptors.